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[Display omitted] Conjugating biomolecules, such as antibodies, to bioconjugate moieties on lipid surfaces is a powerful tool for engineering the surface of diverse biomaterials, including cells and nanoparticles. We developed supported lipid bilayers (SLBs) presenting well-defined spatial distributions of functional moieties as models for precisely engineered functional biomolecular-lipid surfaces. We used quartz crystal microbalance with dissipation (QCM-D) and atomic force microscopy (AFM) to determine how vesicles containing a mixture of 1,2-dipalmitoyl- sn - glycero -3-phosphatidylcholine (DPPC) and 1,2-distearoyl- sn - glycero -3-phosphoethanolamine-N-[azido(polyethylene glycol)-2000] (DSPE-PEG-N 3) form SLBs as a function of the lipid phase transition temperature (T m). Above the DPPC T m , DPPC/DSPE-PEG-N 3 vesicles form SLBs with functional azide moieties on SiO 2 substrates via vesicle fusion. Below this T m , DPPC/DSPE-PEG-N 3 vesicles attach to SiO 2 intact. Intact DPPC/DSPE-PEG-N 3 vesicles on the SiO 2 surfaces fuse and rupture to form SLBs when temperature is brought above the DPPC T m. AFM studies show uniform and complete DPPC/DSPE-PEG-N 3 SLB coverage of SiO 2 surfaces for different DSPE-PEG-N 3 concentrations. As the DSPE-PEG-N 3 concentration increases from 0.01 to 6 mol%, the intermolecular spacing of DSPE-PEG-N 3 in the SLBs decreases from 4.6 to 1.0 nm. The PEG moiety undergoes a mushroom to brush transition as DSPE-PEG-N 3 concentration varies from 0.1 to 2.0 mol%. Via copper-free click reaction, IgG was conjugated to SLB surfaces with 4.6 nm or 1.3 nm inter-DSPE-PEG-N 3 spacing. QCM-D and AFM data show; 1) uniform and complete IgG layers of similar mass and thickness on the two types of SLB; 2) a higher-viscosity/less rigid IgG layer on the SLB with 4.6 nm inter-DSPE-PEG-N 3 spacing. Our studies provide a blueprint for SLBs modeling spatial control of functional macromolecules on lipid surfaces, including surfaces of lipid nanoparticles and cells. [ABSTRACT FROM AUTHOR]

A comparative analysis of the molecular organization and functions allows us to determine typical disorders of the erythrocyte membrane in various pathological processes and conditions. One of the promising methods for measuring the mechanical characteristics of erythrocytes and erythrocyte membranes is atomic force spectroscopy. This scientific article describes an experiment in which three donors took part. Using an atomic force microscope, the stiffness of the erythrocyte membrane was evaluated in the case of control, with the addition of hemin, as well as hemin in combination with perfluorane. It was found that the use of hemen increases the average stiffness of the erythrocyte membrane by 2.1 times, and the subsequent use of perfluorane returns the indicator to its original value. Thus, perfluorane partially restored the initial stiffness in 85% of cases. This method can be effectively used to measure the stiffness of membranes under the action of modifiers of a different nature, as well as in the study of erythrocyte membranes in clinical conditions. [ABSTRACT FROM AUTHOR]

In the present study, the antibacterial and anti-biofilm activity of selenium nanoparticles (SeNPs) produced by Bacillus subtilis BSN313 was investigated. Agar diffusion and microdilution methods did not reveal significant antibacterial activity of SeNPs against P. aeruginosa ATCC 9027, S. typhi ATCC 14028, and S. aureus ATCC 25923 due to the larger size of SeNPs and higher electrophoretic mobility, zeta potential, and/or poor diffusion properties in agar solids. Therefore, the agar overlay method was introduced, and significant antibacterial activity was observed with this method at concentrations (SeNPs) of 200 µg/mL, 150 µg/mL, and 150 µg/mL against P. aeruginosa ATCC 9027, S. typhi ATCC 14028, and S. aureus ATCC 25923, respectively. Atomic force spectroscopy (AFM) results, elucidated the disintegrating effect of SeNPs against Gram-negative (P. aeruginosa ATCC 9027) and Gram-positive (S. aureus ATCC 25923) pathogens. The disintegrating effect of SeNPs was caused by the destruction of the bacterial cell (biofilm producing) by rupturing the cell membrane. The hydrophobicity and zeta potential of the planktonic and biofilm populations were measured. Higher values of hydrophobicity and zeta potential heterogeneity were found for the biofilm population than for the planktonic population. The SeNPs showed significant anti-biofilm activity against biofilm-producing pathogenic strains. The ability of SeNPs to disperse biofilms was greatest at a concentration of 700 µg/mL within 15 min against P. aeruginosa ATCC 9027 (85.7%), S. typhi ATCC 14028 (89.6%), and S. aureus ATCC 25923 (78.3%). While the positive control (ascorbic acid, 32 µg/mL) showed an average dispersion of 95.1% against the biofilms of the strains studied within 90 min. Based on these results, we propose SeNPs as suitable candidates for the treatment of biofilm-producing pathogens. [Display omitted] • Antibacterial and anti-biofilm activities of selenium nanoparticles produced by Bacillus subtilis BSN313. • Agar overlay method, was used for significant antibacterial activity. • Atomic force spectroscopy, elucidated the disintegrative effect of SeNPs against bacteria. • Higher zeta potential values were recorded in biofilm populations as compared to planktonic. • Biogenic SeNPs can be recommended against biofilm producing pathogens in therapeutic and food industries. [ABSTRACT FROM AUTHOR]

SH-SY5Y neuroblastoma cells are widely used to model neurodegenerative disorders like Alzheimer's, Parkinson's, Huntington's, and Hereditary Sensory Neuropathy type 1A (HSN-1A), a peripheral nerve condition causing axon degeneration and sensory loss. A cell model of HSN-1A is developed by overexpressing wild-type and mutant SPTLC1 genes (C133W, C133Y, V144D). Cells are cultured on plastic and gold substrates, with brief electrical stimulation applied to the gold-grown cells. Atomic force microscopy (AFM) is used to measure Young's modulus, indentation, and energy dissipation. Finite Element Method and non-linear modeling validate the results. In the absence of stimulation, mutant cells show lower stiffness compared to non-transfected cells, indicating a direct biomechanical impact of the mutations. Brief electrical stimulation significantly increases the stiffness of mutant cells, particularly in C133W (99%), C133Y (100%), and V144D (111%) variants, despite the mutations. Energy dissipation of stimulated V144D cells decreases to levels comparable to untreated non-transfected cells. The simulations support the AFM measurements, demonstrating that brief electrical stimulation can partially reverse the biomechanical effects of gene mutations., (© 2025 Wiley‐VCH GmbH.)

Cystic fibrosis (CF) is a frequent genetic disease in Caucasians that is caused by the deletion of F508 (ΔF508) in the nucleotide binding domain 1 (NBD1) of the CF transmembrane conductance regulator (CFTR). The ΔF508 compromises the folding energetics of the NBD1, as well as the folding of three other CFTR domains. Combination of FDA approved corrector molecules can efficiently but incompletely rescue the ΔF508-CFTR folding and stability defect. Thus, new pharmacophores that would reinstate the wild-type-like conformational stability of the ΔF508-NBD1 would be highly beneficial. The most prominent molecule, 5-bromoindole-3-acetic acid (BIA) that can thermally stabilize the NBD1 has low potency and efficacy. To gain insights into the NBD1 (un)folding dynamics and BIA binding site localization, we combined molecular dynamics (MD) simulations, atomic force spectroscopy (AFM) and hydrogen-deuterium exchange (HDX) experiments. We found that the NBD1 α-subdomain with three adjacent strands from the β-subdomain plays an important role in early folding steps, when crucial non-native interactions are formed via residue F508. Our AFM and HDX experiments showed that BIA associates with this α-core region and increases the resistance of the ΔF508-NBD1 against mechanical unfolding, a phenomenon that could be exploited in future developments of folding correctors.

Protein folding is a fundamental life process with many implications throughout biology and medicine. Consequently, there have been enormous efforts to understand how proteins fold. Almost all of this effort has focused on water-soluble proteins, however, leaving membrane proteins largely wandering in the wilderness. The neglect has occurred not because membrane proteins are unimportant but rather because they present many theoretical and technical complications. Indeed, quantitative membrane protein folding studies are generally restricted to a handful of well-behaved proteins. Single-molecule methods may greatly alter this picture, however, because the ability to work at or near infinite dilution removes aggregation problems, one of the main technical challenges of membrane protein folding studies.

The aim of this study is to assess the effect of PAMAM dendrimers of second, fourth, and seventh generations on human umbilical vein endothelial cells. Primary endothelial cells were exposed to PAMAM dendrimers for 24 h, using concentrations reducing cellular viability to the levels of 90, 75, and 50%. We assumed, that changes in mechanical properties reflect toxicity of PAMAM dendrimers. The mechanical properties were investigated using atomic force spectroscopy (AFS) technique with the use of two approaches for measuring cell elasticity: global, where the tests were performed using a micrometer-hemispherical probe, and local, where a nanometer-sized probe was used. For the sharp probe, a reduction in the elasticity modulus was observed in comparison to untreated control cells, that is related to the depolymerization of the cytoskeleton and the processes leading to cell apoptosis. In the case of the hemispherical probe, cell softening was also observed in comparison to control cells, but with increasing PAMAM concentrations, the modulus of elasticity increases. It is related to the sensing of numerous intracellular vesicles with the use of this probe, e.g. endosomal and empty plasmalemmal which can also alter cell elasticity. The presence of external and intracellular vesicles was confirmed by scanning and transmission electron microscopy. The relationship between the elasticity of HUVEC cells exposed to PAMAM dendrimers of selected generations and their toxic effects was presented herein for the first time. In the transmission electron microscopy images of the cells exposed to PAMAM dendrimers, we have also observed distinctive vesicles with regular multilayer arranged structure. [ABSTRACT FROM AUTHOR]

Antimicrobial peptides are molecules synthesized by living organisms as the first line of defense against bacteria, fungi, parasites, or viruses. Since their biological activity is based on destabilization of the microbial membranes, a study of direct interaction forces between antimicrobial peptides and biomimetic membranes is very important for understanding the molecular mechanisms of their action. Herein, we use atomic force spectroscopy to probe the interaction between atomic force microscopy (AFM) tips functionalized with magainin 1 and supported lipid bilayers (SLBs) mimicking electrically uncharged membranes of normal eukaryotic cells and negatively charged membranes of bacterial cells. The investigations performed on negatively charged SLBs showed that the magainin 1 functionalized AFM tips are quickly adsorbed into the SLBs when they approach, while they adhere strongly to the lipid membrane when retracted. On contrary, same investigations performed on neutral SLBs showed mechanical resistance of the lipid membrane to the tip breakthrough and negligible adhesion force at detachment. [ABSTRACT FROM AUTHOR]

Endothelial cell aging is related to changes not only in cell phenotype, such as luminal changes, intimal and medial thickening, and increased vascular stiffness, but encompasses different cell responses to various substances including drugs or nanomaterials. In the present work, time‐ and dose‐dependent elasticity changes evoked by silver nanoparticles in endothelial cells in early (below 15) passages were analyzed. Silver nanoparticle concentrations of 3, 3.6, and 16 μg/mL were selected for elasticity measurements for long incubation (24 hours) and of 1 and 3 μg/mL for monitoring dynamic elasticity changes of 1‐, 3‐, and 6‐hour incubations. Surprisingly, a significant reduction in the cells elasticity modulus at lower number of passages exposed to silver nanoparticles used at 3 μg/mL for 24 hours was demonstrated. These results are in contrast to those obtained for endothelial cells in late (33‐43) passages that may result from cellular aging in response to nanosilver. Furthermore, for short incubation times (1 and 3 hours), SNP‐induced significant increase in the cell elasticity modulus was detected. In current work, we also attempted to answer the question whether the changes in cell elasticity were induced by the silver nanoparticles stabilized with polyvinyl pyrrolidone or by stabilizer itself. Elasticity measurements were supplemented by observations made with transmission electron microscopy and scanning electron microscopy, which confirmed the presence of silver nanoparticles inside the cells and on the cell membrane. Additionally, activation of reactive oxygen species was detected for cells exposed to SNPs for 1 and 3 hours, which was accompanied by increased cell elasticity modulus suggesting a possible mechanism of observed phenomenon. [ABSTRACT FROM AUTHOR]

Modifiers of membranes cause local defects on the cell surface. Measurement of the rigidity at the sites of local defects can provide further information about the structure of defects and mechanical properties of altered membranes.The purpose of the study: a step-by-step study of the process of a nonlinear deformation of red blood cells membranes under the effect of modifiers of different physico-chemical nature.Materials and methods. The membrane deformation of a viscoelastic composite erythrocyte construction inside a cell was studied by the atomic force spectroscopy. Nonlinear deformations formed under the effect of hemin, Zn2+ ions, and verapamil were studied.Results. The process of elastic deformation of the membrane with the indentation of a probe at the sites of local defects caused by modifiers was demonstrated. The probe was inserted during the same step of the piezo scanner z displacement; the probe indentation occured at the different discrete values of h, which are the functions of the membrane structure. At the sites of domains, under the effect of the hemin, tension areas and plasticity areas appeared. A mathematical model of probe indentation at the site of membrane defects is presented.Conclusion. The molecular mechanisms of various types of nonlinear deformations occurring under the effect of toxins are discussed. The results of the study may be of interest both for fundamental researchers of the blood cell properties and for practical reanimatology and rehabilitology.

Investigation of mechanical properties of erythrocyte membranes is a pressing issue in practical reanimatology and rehabilitation, because erythrocyte's ability to deform determines the possibility of their passage through capillary network and blood rheology in general.The purpose of the work: to study the process of nonlinear deformation of membranes of normal erythrocytes by the method of atomic force spectroscopy.Materials and Methods. The local stiffness of erythrocyte membranes was studied: that of diskocytes — on the torus and on the depression, that of planocytes — on the cell surface. Аtomic force spectroscopy was used for cell membrane study.Results. The nonlinear deformation process was described by functions h(z), h/z (h), and μ(h). This set of functions describes in full the process of probe incorporation (submergence) into membranes. It has been shown that stepwise dependencies of the stiffness coefficient of membrane segments differ significantly and depend on its condition.Conclusion. The suggested approach may be used in fundamental and clinical studies of blood cells' properties in the norm and different diseases. The method of recording nonlinear deformations may be especially efficient in the reanimatology and rehabilitation practice.

Abstract Background The emerging nanotechnologies have greatly facilitated the development of label-free biosensors. The atomic force microscopy (AFM) has been used to study the molecular mechanism of the reactions for protein and aptamers. The surface plasmon resonance (SPR) have been used in fast detections of various pathogens such as bacteria. This study used both AFM and SPR to investigate the complex reactions between aptamers and outer membrane proteins (OMPs) on the surface of S. typhimurium. Results Two DNA aptamers were used for the label-free detections of S. typhimurium by AFM and SPR. The aptamers have specific binding affinities to the OMPs of S. typhimurium. At single-molecule level, the high resolution AFM topography and recognition images distinguished the OMPs on the bacteria surface, which is the first time the location of individual outer membrane protein have been determined on Salmonella surface. E. coli in the control experiments didn’t generate recognition signals, which proved the specificity of these two aptamers to S. typhimurium. The off-rate values for the interactions of these two aptamers to the OMPs were estimated as 5.2 × 10−3 and 7.4 × 10−3 s−1, respectively, by the AFM dynamic force microscopy (DFS). The force and extension values form DFS measurements were used to distinguish the two aptamers. The surface membrane model was proposed to explain the complex correlations among force and extension values. Next, these two aptamers were used in the bulk solution detections of S. typhimurium. The gold chips in SPR experiments were modified with carboxymethylated-dextran (CD), followed by aptamers immobilization, to reduce the non-specific binding signals. The limit of detection (LOD) was determined as 3 × 104 CFU mL−1. Conclusions The AFM single-molecule study revealed detailed information about the unbinding force and extension of the aptamer in complex biological reactions. The careful analysis of the experimental results provide better understanding of the molecular mechanism of OMPs reactions. The single-molecule measurements are helpful in evaluating the specificity of binding reagents, such as aptamers, in bulk solution detections. The protocols used in the SPR detections can be expanded into the label-free detections of other bacterial pathogens.

The low-intensity ultrasound effects on MCF7 (human breast adenocarcinoma) and MCF10A (healthy breast cells) have been investigated at different sonication protocol to probe the effectiveness and the selectivity of the ultrasound (US) treatment and to understand the implications between cell mortality, biomechanical interactions and cell elastic modulus. Experiments performed at fixed and variable frequency demonstrated the effectiveness of some protocols in killing carcinogenic cells and the healthy cells insensitivity. Variation of elastic properties of MCF7 cells exposed to US under varying sonication conditions was examined. Sonication was carried out at fixed frequency (as it is usually done in therapy protocols), between 400 kHz and 620 kHz, following two protocols: (i) at fixed power output; (ii) at fixed voltage of the US generator. Evolution of cell stiffness during the US treatment was monitored via atomic force spectroscopy (AFS). It was found that cell mortality has a similar trend of variation with respect to sonication frequency regardless of the way specimens are exposed to US. Mechanical properties do not show a uniform trend with respect to frequency, but variations of Young's modulus are more marked near the very low (400–480) kHz or very high frequencies (580–620) kHz. The observed variations may be related to mechanical interactions occurring in the cell culture, suggesting a primacy of the environment on other factors. [ABSTRACT FROM AUTHOR]

Highlights • Adhesion force between MOG and HERV-W proteins and anti-MSRV/HERV-W were similar. • The shapes of force curves presented a typical pattern of a specific interaction. • AFS measurements demonstrate the molecular mimicry hypothesis. • The silver nanoparticles method corroborated the AFS results. • The antigen-antibody interaction was visible to the naked eye by color changing. Abstract Multiple sclerosis (MS) is an autoimmune and inflammatory demyelinating disease of the central nervous system. Experimental evidence supports the reactivity of autoantibodies against components of myelin sheath including the myelin oligodendrocyte glycoprotein (MOG). The MS etiology is still unknown, but some risk factors associated with immune dysregulation, genetic susceptibility, and environmental factors are under investigation. The last consider the hypothesis of molecular mimicry mechanism, which is potentially triggered by viral antigen inducing MS autoimmunity. The Human Endogenous Retroviruses W family (HERV-W) is the subject of studies within this field, based on the detection of HERV-W envelope gene proteins in MS patients' samples. In the biomedical field of diagnosis and therapeutics, nanotechnology is of great use for the detailed study of molecular mechanisms involving specific interactions between biomolecules providing high specificity and sensitivity of response. In view of the significance of etiological aspects for the comprehension of MS mechanisms of action, we applied a nanotechnological approach designed for antibody detection. For this, we analyzed MOG peptide sequences similar to the HERV-W protein. These sequences were subjected to interaction with anti-HERV-W antibodies using atomic force spectroscopy (AFS) and silver nanoparticles (AgNPs) methods to survey the potential occurrence of molecular mimicry. Our results revealed the molecular recognition between the anti-HERV-W antibody and the HERV-W and MOG epitopes by AFS and AgNPs approaches. Specific non-linear shape of force curves and median adhesion force values within the expected range for an antigen-antibody interaction were obtained for HERV-W and MOG peptides, 163 pN and 178 pN, respectively, suggesting the occurrence of cross-reactivity in these systems. [ABSTRACT FROM AUTHOR]

Abstract Atomic Force Spectroscopy (AFS) was conducted on the rough surface of the electrospun porous cellulose acetate fibers to assess the intrinsic hydrophilicity through the molecular interactions between solid surface of the material and the silicon tip of Atomic Force Microscope (AFM). The pull-off force measurement was carried out by a sharp tip rather than a colloidal tip that offers the benefits of nano scale contact area, such as detecting local changes of hydrophilicity in heterogeneous substrates and/or chemically modified surfaces, through precisely selected points from high resolution images. The data were filtered in two steps to eliminate the force-distance curves which were affected by the errors arisen from viscoelastic deformations, drifts, and multicontacts between tip and sample. The proposed refinement procedure would provide an exciting opportunity to overcome the major limitations of interpreting AFS data obtained from nanorough surfaces and advances our knowledge of wetting properties of these surfaces. Graphical abstract Image 1 Highlights • The pull-off force measurement was carried out by a sharp tip that offers the benefits of nano scale contact area. • A methodology was devised to refine data obtained by a sharp tip. • Based on the shape of force-displacement curves, the errors were classified in three groups. • "Slope ratio" index was proposed to quantitatively evaluate the extent of deviation from the ideal contact. • The accuracy of the filtering method was investigated and confirmed by comparison with the results of spin coated films. [ABSTRACT FROM AUTHOR]

Biofouling is a persistent problem in many sectors (healthcare, medicine, marine, and membrane filtration processes). To control the biofouling of surfaces, it is essential to overcome or reduce the adhesion forces between biofilms and surfaces. To access and understand the molecular basis of these interactions, atomic force microscopy (AFM) is a well-suited technology that can measure adhesion forces at the piconewton level. However, AFM-based existing methods only probe interactions between individual cells and surfaces, which is not representative of realistic conditions given that bacteria mainly exist in biofilms. We develop here an original method using FluidFM, a combination of AFM and microfluidics, to probe the adhesion forces between biofilms and filtration membranes modified with an anti-biofouling agent, vanillin. This strategy involves i) growing bacterial biofilms on micrometer-sized polystyrene beads, ii) aspirating these biofilm beads at the aperture of microfluidic cantilevers and iii) using them as probes in force spectroscopy experiments. The results obtained first showed that COOH-functionalized polystyrene beads are more suitable for bacterial growth, and that biofilms obtained after 3 h of incubation could be used with FluidFM. Then, biofilm-scale force spectroscopy experiments showed a significant decrease in adhesion forces, adhesion work, and adhesion events after membrane modification, demonstrating the potential of vanillin-coated membranes to reduce biofouling. In addition, the comparison between results at the individual cell and biofilm scales highlighted the complexity of polymeric matrix unbinding and/or unfolding in the biofilm, showing that individual cells behave differently from biofilms. Overall, this method could have implications in the fields of materials science, chemical engineering, health, and the environment. [Display omitted] • FluidFM was used to probe the interactions between biofilms and membrane surfaces. • Biofilms were grown during 3 h on COOH-functionalized beads. • Beads were aspirated at the aperture of microfluidic AFM cantilevers. • Force spectroscopy showed decreased adhesion of biofilms to treated membranes. • Biofilm adhesion behavior is different than that of single cells. [ABSTRACT FROM AUTHOR]

Ilaria Moscetti,1 Emanuela Teveroni,2,3 Fabiola Moretti,3 Anna Rita Bizzarri,1 Salvatore Cannistraro1 1Biophysics and Nanoscience Centre, Department DEB, Università della Tuscia, Viterbo, Italy; 2Department of Endocrinology and Metabolism, Università Cattolica di Roma, Roma, Italy; 3Institute of Cell Biology and Neurobiology, Consiglio Nazionale delle Ricerche (CNR), Roma, Italy Abstract: Murine double minute 2 (MDM2) and 4 (MDM4) are known as the main negative regulators of p53, a tumor suppressor. They are able to form heterodimers that are much more effective in the downregulation of p53. Therefore, the MDM2–MDM4 complex could be a target for promising therapeutic restoration of p53 function. To this aim, a deeper understanding of the molecular mechanisms underlining the heterodimerization is needed. The kinetic and thermodynamic characterization of the MDM2–MDM4 complex was performed with two complementary approaches: atomic force spectroscopy and surface plasmon resonance. Both techniques revealed an equilibrium dissociation constant (KD) in the micromolar range for the MDM2–MDM4 heterodimer, similar to related complexes involved in the p53 network. Furthermore, the MDM2–MDM4 complex is characterized by a relatively high free energy, through a single energy barrier, and by a lifetime in the order of tens of seconds. New insights into the MDM2–MDM4 interaction could be highly important for developing innovative anticancer drugs focused on p53 reactivation. Keywords: MDM2, MDM4, atomic force spectroscopy, surface plasmon resonance

Objective: to develop a procedure to image native cells in a physiological medium and to measure the local stiffness of fixed red blood cell membranes in liquid in vitro experiments.Material and methods. Blood was taken from 4 healthy donors during prophylactic examinations and placed in EDTA-containing Microvette tubes. The red blood cells were fixed in buffer solution onto a polylysine-coated substrate. Cell images were obtained using an ACM NTEGRA Prima microscope (NT-MDT, the Russian Federation). Membrane stiffness was estimated by atomic force spectroscopy.Results. The values of effective Young's modulus were obtained for a statistical sample of fixed red blood cell membranes. Under the action of verapamil on blood, Young's modulus was equal to 528±21 kP. Under the action of heavy metal ions on blood, the mean local stiffness of the dried membrane was increased up to 942±56 at a depth of 35 nm.Conclusion. The measurements of the force characteristics of red blood cells in liquid can yield reproducible results of examining the elastic properties of the membranes. Atomic force microscopy and atomic force spectroscopy can be employed analyze the properties of a live cell in the physiological medium.

Abstract Soiling of Photovoltaic (PV) modules is a growing area of concern due to the adverse effect of dust accumulation on PV performance and reliability. In this work, we report on four fundamental adhesion forces that take place at the first stage of soiling process. These are capillary, van der Waal, electrostatic and gravitational forces. It is found that under high relative humidity, the adhesion mechanism between dust particles and PV module surfaces is dominated by capillary force, while van der Waal force dominates under dry conditions. Moreover, real field data for long soiling periods over solar panels in Qatar were investigated and resulted in proposing a novel modified sigmoid function that predicts a relative humidity inflexion value at which transition in the particulate matter deposition rate takes place from low to high values. Moreover, the effect of surface roughness was investigated by measuring adhesion force over clean glass versus substrates that are coated with in-house developed anti-dust titania thin films. Highlights • Capillary adhesion force dominates under high relative humidity. • Gravitational adhesion force is negligible for small dust particles. • Novel modified sigmoid function of 18 months of real field data supports domination of capillary force at high RH. • Surface roughness reduces adhesion force. • Anti dust coatings reduces adhesion force. [ABSTRACT FROM AUTHOR]

Abstract Given the increasing trend in bacterial antibiotic resistance, research on antimicrobial peptides and their mechanisms of action has become of huge relevance in the last years. Several studies have investigated the effects of a large variety of antimicrobial peptides directly on bacteria or on model lipid bilayers. In the case of model lipid bilayers, different systems are typically exploited; however, different results could be obtained due to the specific properties of the used system. Supported Lipid Bilayers and Giant Unilamellar Vesicles are among the most popular model systems. Here we used Atomic Force Microscopy and fluorescence microscopy to study the interaction of the antimicrobial peptide Magainin H2, an analog of Magainin 2 with increased hydrophobicity, on Supported Lipid Bilayers. We found that, for this kind of model bilayer, due to its strong interaction with the support, the lateral expansion of the membrane induced by the interaction with the peptides is initially inhibited and subsequently proceeds creating new bilayer regions with many defects. This scenario gives rise in Supported Lipid Bilayers to effects like initial increase of lateral pressure, formation of lipid tubes to release this increase, or development of bilayer regions with lower lipid density. Our results highlight that care should be given to the selected model system when studying and comparing the interaction of peptides with other lipid bilayer model systems. Graphical abstract Unlabelled Image Highlights • Different model systems of lipid bilayers interact differently with Magainin H2. • Magainin H2 interacting with Supported Lipid Bilayer could produce lipid tubes. • At low concentration Magainin H2 produces an increase of the lateral tension in Supported Lipid Bilayers. [ABSTRACT FROM AUTHOR]

Abstract: Endothelial cells, due to their location, are interesting objects for atomic force spectroscopy study. They constitute a barrier between blood and vessel tissues located deeper, and therefore they are the first line of contact with various substances present in blood, eg, drugs or nanoparticles. This work intends to verify whether the mechanical response of immortalized human umbilical vein endothelial cells (EA.hy926), when exposed to silver nanoparticles, as measured using force spectroscopy, could be effectively used as a bio‐indicator of the physiological state of the cells. Silver nanoparticles were characterized with transmission electron microscopy and dynamic light scattering techniques. Tetrazolium salt reduction test was used to determine cell viability after treatment with silver nanoparticles. An elasticity of native cells was examined in the Hanks' buffer whereas fixed cells were softly fixed with formaldehyde. Additional aspect of the work is the comparative force spectroscopy utilizing AFM probes of ball‐shape and conical geometries, in order to understand what changes in cell elasticity, caused by SNPs, were detectable with each probe. As a supplement to elasticity studies, cell morphology observation by atomic force microscopy and detection of silver nanoparticles inside cells using transmission electron microscopy were also performed. Cells exposed to silver nanoparticles at the highest selected concentrations (3.6 μg/mL, 16 μg/mL) are less elastic. It may be associated with the reorganization of the cellular cytoskeleton and the “strengthening” of the cell cortex caused by presence of silver nanoparticles. This observation does not depend on cell fixation. Agglomerates of silver nanoparticles were observed on the cell membrane as well as inside the cells. [ABSTRACT FROM AUTHOR]

The nonlinear interaction between an AFM tip and a sample gives rise to oscillations of the cantilever at integral multiples (harmonics) of the fundamental resonance frequency. The higher order harmonics have long been recognized to hold invaluable information on short range interactions but their utilization has thus far been relatively limited due to theoretical and experimental complexities. In particular, existing approximations of the interaction force in terms of higher harmonic amplitudes generally require simultaneous measurements of multiple harmonics to achieve satisfactory accuracy. In the present letter we address the mathematical challenge and derive accurate, explicit formulae for both conservative and dissipative forces in terms of an arbitrary single harmonic. Additionally, we show that in frequency modulation-AFM (FM-AFM) each harmonic carries complete information on the force, obviating the need for multi-harmonic analysis. Finally, we show that higher harmonics may indeed be used to reconstruct short range forces more accurately than the fundamental harmonic when the oscillation amplitude is small compared with the interaction range.

Photodynamic inactivation (PDI) has been reported to be effective to eradicate a wide variety of pathogens, including antimicrobial-resistant microorganisms. The aim of this study was to identify the potential molecular targets of PDI depending on growth phase of Candida albicans . Fungal cells in lag (6 h) and stationary (48 h) phases were submitted to PDI mediated by methylene blue (MB) combined with a (662 ± 21) nm-LED, at 360 mW of optical power. Pre-irradiation time was 10 min and exposure times were 12 min, 15 min and 18 min delivering radiant exposures of 129.6 J/cm 2 , 162 J/cm 2 and 194.4 J/cm 2 , respectively, on a 24-well plate of about 2 cm 2 at an irradiance of 180 mW/cm 2 . Scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force spectroscopy (AFS) and Fourier transform infrared spectroscopy (FT-IR) were employed to evaluate the photodynamic effect in young and old fungal cells following 15 min of irradiation. Morphological analysis revealed wrinkled and shrunk fungal cell membrane for both growth phases while extracellular polymeric substance (EPS) removal was only observed for old fungal cells. Damaged intracellular structures were more pronounced in young fungal cells. The surface nanostiffness of young fungal cells decreased after PDI but increased for old fungal cells. Cellular adhesion force was reduced for both growth phases. Fungal cells in lag phase predominantly showed degradation of nucleic acids and proteins, while fungal cells in stationary phase showed more pronounced degradation of polysaccharides and lipids. Taken together, our results indicate different molecular targets for fungal cells in lag and stationary growth phase following PDI. [ABSTRACT FROM AUTHOR]

We report on the effect of the first step anodization time on the morphology of TiO 2 nanotube arrays grown by the two-step anodization and their photocurrent response in the backside-illuminated dye-sensitized solar cells. Results show a remarkable increase of tube ordering by increasing the first step anodization time. The Fill factor and open circuit voltage of all dye-sensitized solar cells were approximately 60% and 0.77 V respectively, for a range of first step anodic oxidation from 0.5 to 6 h, whereas the short circuit current increased from 0.94 to 1.57 mA/cm 2 leading to an enhanced photo-to-current efficiency by 73%. According to open circuit voltage decay and electrochemical impedance spectroscopy (the Nyquist and Bode plots), we attributed such an enhanced cell performance to lower recombination rates due to higher ordered TNAs associated with the actual surface area and coherency of the cells' components. [ABSTRACT FROM AUTHOR]

Background Mutations within the DNA binding domain (DBD) of the tumor suppressor p53 are found in > 50% of human cancers and may significantly modify p53 secondary structure impairing its function. p28, an amphipathic cell-penetrating peptide, binds to the DBD through hydrophobic interaction and induces a posttranslational increase in wildtype and mutant p53 restoring functionality. We use mutation analyses to explore which elements of secondary structure may be critical to p28 binding. Methods Molecular modeling, Raman spectroscopy, Atomic Force Spectroscopy (AFS) and Surface Plasmon Resonance (SPR) were used to identify which secondary structure of site-directed and naturally occurring mutant DBDs are potentially altered by discrete changes in hydrophobicity and the molecular interaction with p28. Results We show that specific point mutations that alter hydrophobicity within non-mutable and mutable regions of the p53 DBD alter specific secondary structures. The affinity of p28 was positively correlated with the β-sheet content of a mutant DBD, and reduced by an increase in unstructured or random coil that resulted from a loss in hydrophobicity and redistribution of surface charge. Conclusions These results help refine our knowledge of how mutations within p53-DBD alter secondary structure and provide insight on how potential structural alterations in p28 or similar molecules improve their ability to restore p53 function. General significance Raman spectroscopy, AFS, SPR and computational modeling are useful approaches to characterize how mutations within the p53DBD potentially affect secondary structure and identify those structural elements prone to influence the binding affinity of agents designed to increase the functionality of p53. [ABSTRACT FROM AUTHOR]

Atomic force spectroscopy, a technique derived from Atomic Force Microscopy (AFM), allowed us to distinguish nonspecific and specific interactions between the acetolactate synthase enzyme (ALS) and anti-atrazine antibody biomolecules and the herbicides imazaquin, metsulfuron-methyl and atrazine. The presence of specific interactions increased the adhesion force (Fadh) between the AFM tip and the herbicides, which made the modified tip a powerful biosensor. Increases of approximately 132% and 145% in the Fadh values were observed when a tip functionalized with ALS was used to detect imazaquin and metsulfuron-methyl, respectively. The presence of specific interactions between the atrazine and the anti-atrazine antibody also caused an increase in the Fadh values (approximately 175%) compared to those observed when using an unfunctionalized tip. The molecular modeling results obtained with the ALS enzyme suggest that the orientation of the biomolecule on the tip surface could be suitable for allowing interaction with the herbicides imazaquin and metsulfuron-methyl.

The use of agrochemicals has increased considerably in recent years, and consequently, there has been increased exposure of ecosystems and human populations to these highly toxic compounds. The study and development of methodologies to detect these substances with greater sensitivity has become extremely relevant. This article describes, for the first time, the use of atomic force spectroscopy (AFS) in the detection of enzyme-inhibiting herbicides. A nanobiosensor based on an atomic force microscopy (AFM) tip functionalised with the acetolactate synthase (ALS) enzyme was developed and characterised. The herbicide metsulfuron-methyl, an ALS inhibitor, was successfully detected through the acquisition of force curves using this biosensor. The adhesion force values were considerably higher when the biosensor was used. An increase of ~250% was achieved relative to the adhesion force using an unfunctionalised AFM tip. This considerable increase was the result of a specific interaction between the enzyme and the herbicide, which was primarily responsible for the efficiency of the nanobiosensor. These results indicate that this methodology is promising for the detection of herbicides, pesticides, and other environmental contaminants.

This review article discusses and documents the basic concepts and principles of nano/biosensors. More specifically, we comment on the use of Chemical Force Microscopy (CFM) to study various aspects of architectural and chemical design details of specific molecules and polymers and its influence on the control of chemical interactions between the Atomic Force Microscopy (AFM) tip and the sample. This technique is based on the fabrication of nanomechanical cantilever sensors (NCS) and microcantilever-based biosensors (MC-B), which can provide, depending on the application, rapid, sensitive, simple and low-cost in situ detection. Besides, it can provide high repeatability and reproducibility. Here, we review the applications of CFM through some application examples which should function as methodological questions to understand and transform this tool into a reliable source of data. This section is followed by a description of the theoretical principle and usage of the functionalized NCS and MC-B technique in several fields, such as agriculture, biotechnology and immunoassay. Finally, we hope this review will help the reader to appreciate how important the tools CFM, NCS and MC-B are for characterization and understanding of systems on the atomic scale.

β 2 -Microglobulin (B2M) is a human protein involved in the regulation of immune response and represents a useful biomarker for several diseases. Recently, anti-B2M monoclonal antibodies have been introduced as innovative therapeutic agents. A deeper understanding of the molecular interaction between the two partners could be of utmost relevance for both designing array-based analytical devices and improving current immunotherapies. A visualization at the nanoscale performed by Atomic Force Microscopy revealed that binding of B2M to the antibody occurred according to two preferred interaction geometries. Additionally, Atomic Force Spectroscopy and Surface Plasmon Resonance provided us with detailed information on the binding kinetics and the energy landscape of the complex, both at the single molecule level and in bulk conditions. Combination of these complementary techniques contributed to highlight subtle differences in the kinetics behaviour characterizing the complexes. Collectively, the results may deserve significant interest for designing, development and optimization of novel generations of nanobiosensor platforms. [ABSTRACT FROM AUTHOR]

Force fluctuations recorded in an atomic force spectroscopy experiment, during the approach of a tip functionalized with biotin towards a substrate charged with avidin, have been analyzed by a wavelet transform. The observation of strong transient changes only when a specific biorecognition process between the partners takes place suggests a drastic modulation of the force fluctuations when biomolecules recognize each other. Such an analysis allows to investigate the peculiar features of a biorecognition process. These results are discussed in connection with the possible role of energy minima explored by biomolecules during the biorecognition process. [ABSTRACT FROM AUTHOR]

A fundamental understanding of biofilm mechanical stability is critical in order to describe detachment and develop biofouling control strategies. It is thus important to characterise the elastic deformation and flow behaviour of the biofilm under different modes of applied force. In this study, the mechanical properties of a mature wastewater biofilm were investigated with methods including macroscale compression and microscale indentation using atomic force microscopy (AFM). The mature biofilm was found to be mechanically isotropic at the macroscale level as its mechanical properties did not depend on the scales and modes of loading. However, the biofilm showed a tendency for mechanical inhomogeneity at the microscale level as indentation progressed deeper into the matrix. Moreover, it was observed that the adhesion force had a significant influence on the elastic properties of the biofilm at the surface, subjected to microscale tensile loading. These results are expected to inform a damage-based model for biofilm detachment. [ABSTRACT FROM PUBLISHER]

Analytical possibilities of atomic force spectroscopy (AFS) in liquid were studied upon interaction of membranotropic polymers with the plasma membrane of human cells. Topographical visualization of tightly adherent dermal fibroblasts, but not relatively soft prostate cancer (PC-3) cells, was achieved using a conventional triangular cantilever. A microsphere-based probe has been developed and applied for AFS analysis of micromechanical properties of PC-3 cells. Non-ionic block copolymers of ethylene oxide and propylene oxide, bi-functional Pluronic® L61, and glycerol-based tri-functional copolymer (TFC) were studied as potential modulators of cellular membranes and drug delivery systems as reported by Bondar et al. (Int. J. Pharm. 461(97), 104, ). As indicated by dynamic light scattering and fluorescent techniques, Pluronic® L61 and TFC were adsorbed onto the cell surface and inserted into the plasma membrane in different extent. Analysis of AFS curves for surfactant-treated PC-3 cells showed that both Pluronic® L61 and TFC decreased the Young's modulus of cellular surface by almost 1.6 and 2 times, respectively. This is in accordance with the ability of amphiphilic polymers of decreasing the microviscosity of cellular membrane and promoting intracellular drug uptake as shown previously by Bondar et al. (Int. J. Pharm. 461(97), 104, ). Our results are of particular interest for the characterization of interaction of living cells with amphiphilic polymer-based nanocarriers and drug formulations using AFS and other surface-sensitive techniques. [ABSTRACT FROM AUTHOR]

Molecular layer-by-layer (mLbL) deposition of highly crosslinked polyamide-based membranes affords flexibility and control over membrane properties such as thickness, roughness, and chemistry of the selective membrane layer. Of particular interest is the ability to non-destructively tailor the surface chemistry of the membrane for a particular purpose, such as enhancing hydrophilicity or minimizing membrane fouling. Here, we show that the surface chemistry of the mLbL membrane can be tuned via termination reactions to render the surface rich in –COOH, −NH 2 , −polyethylene glycol (−PEG), or −fluorinated groups. We systematically characterize the resulting surfaces with X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) to validate successful modification and to ensure the low surface roughness is maintained, respectively. We then use pH-dependent contact angle and carboxylate-modified colloidal probe AFM to measure the surface wettability and adhesion of the modified surfaces. The measured adhesion force follows the ranking –NH 2 ≫ −fluorinated > –COOH ≈ −PEG, where the –COOH and −PEG are repulsive due to charge interactions and hydration state, respectively. Combined with the low surface roughness afforded by mLbL deposition, surface functionalization through termination reactions as shown here will allow researchers to disentangle contributions of surface chemistry from surface roughness to the overall performance and fouling of polyamide-based membranes for water purification and advanced chemical separations. [Display omitted] [ABSTRACT FROM AUTHOR]

Reliable quantification of a cell's biophysical properties is key for understanding the role of mechanics in cell biology. Plasma membrane tension, the energetic cost of increasing the surface area of the plasma membrane, has been shown to regulate a plethora of cellular processes, ranging from leading edge formation to phagocytosis and membrane trafficking. Here, we describe the measurement of this key mechanical property of the cell surface using atomic force microscopy (AFM)-based force spectroscopy. Depending on the nature of the force curve acquisition, AFM measurements can quantify various membrane tension components, such as apparent membrane tension and membrane-to-cortex attachment (MCA). We discuss the biophysical background (1), required materials (2), sample preparation (3.1), AFM-probe calibration and functionalization (3.2), force curve acquisition (3.3) and data analysis and representation (3.4)., (© 2023. The Author(s), under exclusive license to Springer Science+Business Media, LLC, part of Springer Nature.)

A strain-sensing lyriform organ (HS-10) found on all of the legs of a Central American wandering spider ( Cupiennius salei ) detects courtship, prey and predator vibrations transmitted by the plant on which it sits. It has been suggested that the viscoelastic properties of a cuticular pad directly adjacent to the sensory organ contribute to the organ’s pronounced high-pass characteristics. Here, we investigate the micromechanical properties of the cuticular pad biomaterial in search of a deeper understanding of its impact on the function of the vibration sensor. These properties are considered to be an effective adaptation for the selective detection of signals for frequencies >40 Hz. Using surface force spectroscopy mapping we determine the elastic modulus of the pad surface over a temperature range of 15–40 °C at various loading frequencies. In the glassy state, the elastic modulus was ∼100 MPa, while in the rubbery state the elastic modulus decreased to 20 MPa. These data are analyzed according to the principle of time–temperature superposition to construct a master curve that relates mechanical properties, temperature and stimulus frequencies. By estimating the loss and storage moduli vs. temperature and frequency it was possible to make a direct comparison with electrophysiology experiments, and it was found that the dissipation of energy occurs within a frequency window whose position is controlled by environmental temperatures. [ABSTRACT FROM AUTHOR]

Abstract: Background: TP53 tumor suppressor gene is mutated in more than 50% of human tumors. Mutated p53 proteins could sequestrate and inactivate p73 reducing the apoptotic and anti-proliferative effects of the transcription factor, and yielding cancer cells more aggressive and chemoresistant. The possibility of using drugs to prevent the mutant p53/p73 complex formation preserving the p73 function, calls for a deeper insight into the molecular and biochemical mechanisms of mutant p53/p73 protein interaction. Methods: The kinetics of the mutant p53R175H/p73 complex was investigated with innovative and complementary techniques, operating in real time, in near physiological conditions and without any labeling. Specifically, Atomic Force Spectroscopy and Surface Plasmon Resonance working at single-molecule level and in bulk condition, respectively, were used. Results: The two techniques revealed that a stable complex is formed between mutant p53R175H and p73 proteins; the complex being characterized by a high interaction force and a dissociation equilibrium constant in the order of 10−7 M, as expected for specific interactions. No binding was instead observed between p73 and wild type p53. Conclusions: Mutant p53R175H protein, unlike wild type p53, can form a stable complex with p73. The mutant p53R175H/p73 protein complex could be a target for innovative pharmaceutical drugs that, by dissociating it or preventing biomolecule interaction thus preserving the p73 function, could enhance the response of cancerous cells carrying mutant p53R175H protein to common chemotherapeutic agents. General significance: The kinetic information obtained in vitro may help to design specific pharmaceutical drugs directed against cancerous cells carrying mutant p53 proteins. [Copyright &y& Elsevier]

Highlights: [•] Innovative CVD technique used to deposit ultra-thin PMMA membranes. [•] Indirect and direct characterization of a polymeric ultra-thin film. [•] Liquid monomer encapsulation as blisters in an ultra-thin polymer membrane. [•] Self-healing behavior under laser irradiation. [ABSTRACT FROM AUTHOR]